1. Field of the Invention
The invention relates to papermakers felts and methods of their manufacture and more particularly relates to felts useful in the press section of a papermaking machine.
2. Brief Description of the Prior Art
The modern papermaker employs a highly sophisticated machine to make paper, which is named rather appropriately a "papermaking machine". The modern papermaking machine is in essence a device for removing water from the paper furnish. The water is removed sequentially in three stages or sections of the machine. In the first or forming section, the furnish is deposited on a moving forming wire and water drained through the wire to leave a paper sheet or web having a solids content of circa 18 to 25 percent by weight. The formed web is carried into a wet press felt section and passed through one or more nip presses on a moving press felt to remove sufficient water to form a sheet having a solids content of 36 to 44 percent by weight. This sheet is then transferred to the dryer section of the papermaking machine where dryer felts press the paper sheet against hot, steam-heated dryer cylinders to obtain a 92 to 96 percent solids content.
The clothing employed on the paper making machine must perform a widely diverse range of functions, according to the position on the machine, i.e.; forming, press or dryer section. In view of the diversity of functions, the clothing for use in each section of the machine must be manufactured to meet specific design requirements essential to the particular section. In the absence of meeting the specific felt design requirements demanded in each section of the machine, the overall operation of the machine will be unsatifactory. Optimum operating lives of the felts will not be achieved, product quality may be adversely affected, machine speeds may be lowered or drying efficiency may be impeded.
Prior to the present invention, one of the problems associated with papermaking efficiency has been "wad burning" of press felt fabrics in the press section of the papermaking machine. Wad burning occurs when a wad of the formed web entering a press nip in the wet press section lodges at the entrance to the nip. The lodged wad creates a high frictional force against the press felt fabric. The heat of friction generated may melt and fuse synthetic fibers in the surface of the press felt, thereby causing areas in the felt which do not allow water to drain. Wad burning damage has become much more prevalent with synthetic felts used on hihgly loaded presses (above 600 psi or 42.2 kg/cm.sup.2) usually found in the second and third positions of the wet press section. Wad burning damage can be reduced to some degree by fabricating the press felts from high temperature resistant materials or by including high proportions of wool in the fabric. However, wad burning prior to the present invention has not been completely eliminated as a problem since even high temperature resistant fibers such as polyaramid fibers are degraded by wad burning.
By the method of the present invention, synthetic fiber surfaces containing press felt fabrics, particularly of the "Batt-on-Base" type construction, i.e.; press fabrics comprising a textile fabric base and a batt surface attached by needling, are made resistant to wad burning. The felts of the invention also exhibit enhanced abrasion resistance, reduced fiber shedding and overall longer operating lives.